1. Field of the Invention
This invention relates to an apparatus for milling lumber. More specifically, it relates to cutterhead design for flake-cutting.
2. Prior Art
Simpler cutterhead designs have been proposed by others; for example, those helical cutterheads which cut on a common cutting circle. (See Stewart, H. A., "Chips produced with a helical cutter," Forest Products Journal 21(5):44; and Stewart, H. A., and Lehmann, W. F., "Crossgrain cutting with segmented cutters produces good surfaces and flakes," Forest Products Journal 24(9) :104.) Another previous cutterhead design is that of D. L. Schubert (see U.S. Pat. No. 2,898,958).
Headrig and edger chippers cutting in the 90-0 and 90-90 modes are in widespread use if softwood mills of North America (Koch, P., "Utilization ofthe Southern Pines," USDA Agriculture Handbook 420, p. 836) and to a lesser extent throughout the rest of the world. They have been adopted because of their productivity per man-hour and because they make no sawdust.
Because their peripheral-milling and end-milling cutterheads take large bites per tooth to make pulp chips 5/8- to 7/8-inch in length, they tear out grain around knots and tend to splinter board edges. Resultant surfaces display torn grain extending perhaps 1/8-inch into board face or edge.
These torn rough lumber surfaces can, for the most part, be smoothed if planers are adjusted to remove about 1/8-inch from board faces and edges. Because of the low value of planer shavings, lumbermen are reluctant to take this remedial action, however.
It therefore appears virtually mandatory that the next generation of chipping headrigs and chipping edgers be equipped with cutterheads that leave smooth surfaces. Mills equipped with such cutterheads acting in concert with multiple bandsaws can produce quality lumber with minimum labor input, and minimum output of low-value sawdust and shavings.